This is exactly why HTML is so ubiquitous, because it is so tolerant of mistakes in formatting, syntax, and just about anything else.
Most browsers will even read and process most of the things listed on this page because even if the spec doesnt say so, it just makes sense to anyway.
Is HTML that way because of it being HTML, or have browsers just decided to brute force their way into handling the slop so that people won't blame the browser for not doing it correctly?
React.js with JSX (which people use to avoid writing HTML) is basically the opposite on its tolerance for mistakes but somehow it seems pretty popular, to say the least.